In recent years, technological development of the following has been advanced: input circuits capable of inputting data when light is incident thereon, input-output devices capable of inputting data when light is incident thereon and performing output in accordance with the input data, and the like.
Examples of the input circuits include touch panels incorporating image sensors or photosensors. The image sensors generally include CCD sensors and CMOS sensors. The CCD sensors are image sensors that perform charge transmission by vertical CCD and parallel CCD. The CMOS sensors are image sensors manufactured through a CMOS process. The CMOS sensors can control a reading operation of charge for each pixel with the use of switches of MOS transistors (for example, Patent Document 1).
Examples of the input-output devices include an input-output device incorporating photosensors (for example, Patent Document 2). The input-output device incorporating photosensors can function as a touch panel when each pixel portion is provided with a display circuit and a photodetector circuit (also referred to as a photosensor) and the photodetector circuit detects the illuminance of light incident on the pixel portion. Further, the input-output device incorporating photosensors can also change display states in accordance with detection results obtained by the photodetector circuits. For example, by using the touch panel, a figure such as an alphabet written on the touch panel can be displayed as input text data.